To make the fish, grease the slow cooker with butter or cooking spray. Arrange the onion slices in a layer covering the bottom of the pot.
Arrange the salmon in a single layer on top of the onions.
In a small bowl, stir together the wine, lemon juice, salt, pepper, and garlic. Pour the mixture over the fish.
Cover the slow cooker and cook on low for two hours. The salmon should be cooked through and flake easily with a fork.
To make the herb salsa, in a small bowl, mix together the shallot and vinegar, and let the mixture stand for 15 to 20 minutes.
In a separate small bowl, mix together the parsley, chives, olive oil, salt, and pepper. Strain the shallots, reserving the vinegar, and add them to the herbs. Add a teaspoon or two of the vinegar to the mixture to taste.
Serve the fish with the salsa spooned over the top.
